A burst supply line on a washing machine pumps roughly 600 gallons an hour onto your floor. The single most useful thing you can do as a homeowner — more useful than any tool — is know where your main shutoff is and confirm it actually works. Do this once and tell everyone in the house.
Find the main shutoff
It's almost always in one of these places:
- Basement: on the wall facing the street, near where the supply line enters the foundation.
- Crawl space: same wall as the basement version, just lower.
- Garage: against the wall closest to the street, often near the water heater.
- Outside (warm climates): a green or black plastic lid in the ground near the street, marked with a "W". You'll need a water key — a long T-shaped tool — to operate the curb stop inside.
- Utility closet (apartments and condos): behind an access panel near the water heater or laundry.
Know which kind of valve you have
Ball valve: a lever handle. Quarter turn — when the lever is across the pipe, the water is on; perpendicular to the pipe, off. These are reliable.
Gate valve: a round wheel handle. Turn clockwise to close. Many turns. Old gate valves seize after years of disuse and can break when forced. If yours is more than 20 years old and has never been operated, it's worth replacing with a ball valve as preventive maintenance.
Test it now
- Open a faucet upstairs.
- Close the main valve.
- Watch the faucet — water should taper off and stop within 30 seconds.
- Open it back up. If the valve is stiff or leaks when you turn it, schedule a replacement before you need it.
Local shutoffs you should also know
Sometimes the main is overkill. Most fixtures have their own valve:
- Toilets: small valve on the wall behind, where the supply line meets the tank.
- Sinks: two valves under the sink, one for hot and one for cold.
- Washing machine: two valves on the wall behind the machine. Close them when you go on vacation — supply hoses are the #1 cause of household water damage.
- Water heater: a valve on the cold-water inlet at the top of the tank.
If a pipe bursts
- Close the main shutoff first. Don't try to find the local one — every second is gallons.
- Cut power to the affected area at the breaker if water is near outlets, fixtures, or the panel.
- Open a faucet on the lowest floor to drain the line and stop the flood faster.
- Call a plumber. We're 24/7.
One more thing: take a phone photo of your main valve and where it is, and text it to everyone in the household. When the moment comes, nobody is calm enough to remember.